The hydraulic cement industry has utilized, in cement formulations, various ashes which are essentially waste products or by-products of production processes for several desired goals, the most obvious of which is to utilize an ever-growing source of material while at the same time lessening the ecological burden. Prior art has continued this evolution to the point of development of cement binders made exclusively from ash materials, with little or no portland cement as a constituent. What has evolved are high early strength hydraulic cements that are used for limited special applications.
These mineral binders and their progeny, have been developed with emphasis on dry interground or interblended formulation which is then mixed in water to produce an activated binder. The problem of intergrinding or interblending presents itself in the form of increased cost because of the need to transport the raw materials for making the binder to a central location where the grinding and manufacturing can take place.
The formulations of these prior art binders present a number of difficulties and limitations to the user. In each, there is an inherent failing: the water which is introduced into the binder material is needed to serve the purpose of properly dissolving and dispersing each element of the composition so that it may interact with the balance of the elements; however, the hydration reaction which is the ultimate goal begins to occur at the moment the water is introduced. When the objective is to produce high early strength cements, the problem of mixing is compounded by the need to include accelerators, activators, and retarders. Not only does the hydration reaction begin with the addition of water, but the water is also what starts the accelerators, activators, and retarders to interact with one another, and, the cementitious components, thereby affecting how fast or how slow the hydration proceeds. This prior art method, with limited amount of time, presents difficulty when the binder is put to practical applications. The user has an ever-decreasing amount of time to mix, transport and place the material properly. Time is so short that on-site mixing becomes imperative and only special applications that can afford the extra cost involved can use these cements. Although recent developed cements have provided high early strengths, the loss of working time was an unfortunate consequence of what was accomplished. Such cements are described in Heitzmann et al., U.S. Pat. No. 4,842,649, issued Jun. 27, 1989, and Gravitt et al., U.S. Pat. No. 4,997,484, issued Mar. 5, 1991, respectively.
Further, these prior art cement binders exhibit a premature exothermic reaction during mixing as portions of the binder agglomerate or "ball". When these binders are used for making structural mortars and concretes on a large scale (such as in a ready-mix truck or an industrial batch operation), agglomeration or "balling" could have disastrous effects upon the equipment unless the mixer is only partially filled. After mixing for a few minutes the reaction subsides and the mix smoothes out.
All of the prior art high early strength cements, stress the necessity of low water/cement ratio, which results in low slump, and is difficult to place. Another consequence of low water/cement ratio is inadequate bleed water for the finisher to trowel the mixture properly.
Also the cement binder as described in U.S. Pat. No. 4,997,484, does not appear to provide adequate abrasion resistance for structural applications.
What prior art has not recognized is the value which each element of the composition can impart when introduced individually. Many prior art compositions contain material elements which are somewhat mutually exclusive, and are referred to in the prior art as retarders and activators or accelerators. Logic would not dictate that efficient use of either could be obtained by activating both at the same moment. This is particularly significant since some of the material components referred to by the industry as retarders actually provide significant additional functional value, undiscovered in prior art.
Prior art describes the use of citric acid as a retarder. The confusion over what role citric acid actually plays is probably the reason why previous attempts to control the hydration reaction of cements containing large quantities of subbituminous fly ash have had such erratic results. In the field of high percentage fly ash binders which are formulated as high early strength hydraulic cements, citric acid can play a role more aligned with an accelerator. Prior art usage has failed to recognize this phenomenon and consequently, in some cases has attempted to utilize citric acid as a retarder where the formulation design could only cause the citric acid used to exhibit itself as an accelerator.
Such cement binders are described in U.S. Pat. No. 4,997,484, respectively.
Prior art has also failed to provide for a composition of material which would allow the user to control the initial set of the material at the location of use. The consequence of this failing, when considered together with the very limited amount of working time provided by prior art binders, is that they may only be used in special applications on a small scale. Since high volume use requires machinery intensive production processes, users require materials with a greater degree of flexibility in order to minimize the risks associated with cement binders producing high early strength hardened masses.
The present invention addresses the need for a rapid strength gaining, hydraulic cement by providing a composition of materials which are introduced by mixing sequences to provide:
1. time to mix all the ingredients properly, PA1 2. unrestricted time to transport the mixture of cementitious components, water and aggregates with the ability to terminate the time when it is not needed, PA1 3. high early strength cements with high slump mixes that are easy to place and finish, and, PA1 4. placement and finishing time period that can be short or long depending on the applications, with the added flexibility, to make a selection at the job site. PA1 1. removing unburnt carbon, if it prevents the use of fly ash that contains excessive amounts, PA1 2. improving the density to reduce the permeability, and, PA1 3. increasing the abrasion resistance, PA1 4. eliminating or minimizing alkali silica reactivity if the elements which contribute to this problem are present, and PA1 5. creating a more durable, more cost-effective, general purpose, structural cement. PA1 (1) The increased effectiveness of lithium as an alkali metal activator enables less quantity to be used; thereby, providing the maker of the cement with equal or better benefits at less cost. PA1 (2) Since the alkali metal activator is accelerated with approximately an equal amount of citric acid accelerator, which has previously accounted for nearly half of the total cost of the chemical components, the ability to use less activator also enables the maker of the cement to use less accelerator which in turn further reduces the overall cost. PA1 (3) Reducing the amount of the activator and accelerator in turn enables the set-suspending and modifying retarder to be reduced while still maintaining the desired amount of placement time. PA1 (4) Since less volume of both the lithium activator and citric acid accelerator are required to terminate the set-suspended cementitious components, and these activating components must logically be transported to the point where the activation takes place, then both the size of the containers required, and the means to convey the chemical components can be reduced; thereby, enabling the maker of the cement to provide equal or better benefits at another reduction in cost. PA1 (5) As Ex. 36 compared to Ex. 37, 38, 39 demonstrate, the combined use of the alkali metal activators enables the cement maker to substantially reduce the quantity of the activator and accelerator used to obtain increased placement time after activation instead of using more borax and boric acid which again further reduces the cost. PA1 (6) Both sodium hydroxide and potassium hydroxide are extremely deliquescent. Storage and pneumatic conveyance of these materials must take this characteristic into account. Lithium hydroxide is not deliquescent. PA1 (7) As revealed in the chloride permeability test included in the parent patents, U.S. Pat. Nos. 5,387,283 and 5,374,308 and redone by the CORPS for the FHWA, this blended hydraulic cement mortar is exceptionally dense. It has long been known that adding lithium hydroxide and carbonate is an excellent means for making concrete less permeable. Less lithium will be required to obtain this benefit; because, a cement with a denser pore structure, as measured by its resistance to the passage of chloride, does not require as much water inhibiting agent to achieve equal or better resistance to permeability.
A further method of this invention is to improve the physical properties of waste fly ash so they can be used more productively to create both general purpose as well as special application blended hydraulic cements by:
Prior art teaches away from the present invention when U.S. Pat. No. 4,842,649, states the order of mixing the various materials that make up the composition is immaterial, and, U.S. Pat. No. 4,997,484, states that all the components can be interground or interblended and that doing so eliminates the control problems that can occur.